This invention relates to adjustable mounting technology and more particularly to adjustable mechanisms which can be used in evacuated cryogenic environments.
Research measurements of trace gas species in the stratosphere for the purpose of understanding the physics and chemistry of the upper atmosphere require the use of highly sensitive instruments. Typically these instruments use sensitive electro-optical transducers for the detection and identification of tenuous atmospheric constituents by spectroscopic or other means. The extreme sensitivity of these devices generally requires that the transducer be cryogenically cooled and housed in evacuated chambers for isolation from the ambient temperature. In addition, precise alignment of elements in the detector device are required. The use of a photo detector, for example, requires an external collimated light beam to be focused on the transducer. Other examples, such as semiconductor laser elements require focusing a coherent light source through a lens into a collimated reference signal. All techniques require that the electro-optical transducer be accurately aligned and positioned with respect to a fixed focus lens which provides the interface between the transducer in the evacuated chamber and the external optical system. The transducer must be aligned linearly along a reference three-axis coordinate system with respect to the optical axis and focal point of the lens. In addition, the transducer must be aligned through two angles with respect to the reference coordinate system to assure optimum radiation exchange between the transducer and the optical system. Only two angular adjustments are incorporated; the third angle must be fixed in order to preserve the alignment of optical polarization between the transducer and the external optical system. This angular adjustment is particularly critical for optimally focusing a semiconductor laser element which may radiate field patterns which are angularly misaligned with respect to the crystal face. Atmospheric researchers using transducer detection devices need a means to provide at least five degrees of freedom, there in translation and two in rotation, in order to properly adjust the electro-optical transducer. These adjustments must be made while the transducer is sealed in an evacuated and cryogenically cooled environment.
Prior adjustable mounts have been unsuitable due to a lack of adjustment sensitivity, lack of mechanical stability which allows vibrational errors, lack of isolation from ambient temperature, and lack of dimensional stability due to thermal contraction or expansion of the mechanism.
Although fixed mountings used in prior art avoided the above problems, the lack of adjustability results in unsatisfactory operation of the detection devices. Linear adjustments in three dimensions are necessary for proper alignment of the lens location in the lateral and axial directions with respect to the external optical system and the internal transducer. Fine adjustments, on the order of 25 micro-meters are required. Since these adjustments are not provided by the prior art, the necessary alignments must be provided externally and may require a reorientation of external optical system components or may result in some basic misalignment of the system. A significant feature of the present invention is that appropriate linear adjustments can be made during system operations until the optical response is optimized.
Prior art provides a fixed-lens system without any provision for angular adjustments of the electro-optical transducer. Semiconductor lasers, however, often produce irregular far field radiation patterns wherein much of the radiated energy is concentrated off-center in one or more lobes. A fixed angle lens cannot position the higher energy lobes on the transducer.
A further difficulty with prior art fixed mounting is that a window must be used rather than a focusing lens because of the absence of internal adjustments. This configuration requires the use of an external lens to collect widely dispersed energy from the diode resulting in a loss of scattered energy and a loss of overall system efficiency. Positioning of an external lens also requires reorientation of the entire optical system to accept the variable optical axis location defined by the lens.
Another significant disadvantage of prior art, when both a window and lens are used, involves the resultant refractive attenuation of the signal caused by using two optical elements in series. With certain low power semiconductor lasers, this additional signal loss can be significant. Further, often the external alignment process is complicated by the use of window material which is opaque to visible light, making a visual alignment of the external optical elements impossible.
Accordingly, it is an object of the present invention to provide a means for precise and remote positioning of electro optical transducers which are housed in cryogenic, evacuated environments.
It is a further object of the present invention to provide a means for accurate, temperature-controlled cryogenic cooling of the adjustable mounted transducer.
It is yet another object of the present invention to provide a means of efficient thermal isolation of the mount from the adjustable base.
Still another object of the present invention is to provide a means for remote adjustment while maintaining vacuum integrity between the evacuated transducer and the ambient environment.
A further object of the present invention is to provide a means for efficient thermal shielding of the electro optical transducer which increases the efficiency of transducer cooling.